Interpretive Summary: Reproductive success is vitally important to the economic success of beef producers. However, few tools are available for beef producers to assess genetic potential for fertility related traits. Here we develop a new paradigm for a system of national cattle evaluation that focuses explicitly on sustained reproductive success of beef females. Data used in this study result from the inventory based reporting system of the American Hereford Association. There were 36,866 females contributing to this analysis with 14,143 of these remaining in production at the time of this analysis. There were 3,323 sires that had daughters with records. Heritability of sustained reproductive success on the underlying scale estimated from these data was approximately 0.05. Additional data accumulated over time will improve this genetic evaluation. Sustained reproductive success is important to the commercial beef industry and results from this evaluation are expected to enhance the assessment of economic value of Hereford seedstock.

Technical Abstract:
The objective of this research was to develop a prototype system for national cattle evaluation that would facilitate selection for improved fertility of daughter from Hereford sires. Raw data for this analysis were birth dates of calves as reported to the American Hereford Association (AHA) by breeders. Records from females entered into this analysis with the reporting of a birth date for their first calf. At this time, females were required to be in contemporary groups of at least three animals and have at least two additional paternal half-sibs also represented in the data. To explicitly define “sustained reproductive success” the philosophy taken was that a female that maintains a calving interval of 425 days or less would be considered successful. Females failing to meet this criterion were considered at the end of their successful lifetime. Data were analyzed using methodology for survival analysis with grouped data. Fixed contemporary groups were modeled as being time-dependent reflecting the females exposed for breeding in the same herd-year-season. Sire effects were time-independent and considered random. Also included in the analysis were time-independent covariates for maternal weaning weight and total maternal calving ease from the national cattle evaluation of AHA. Records from females still successfully in production at the time of this analysis, those that were transferred, those with calving intervals less than 280 d, and those that were successful until becoming donor dams for embryo transfer were considered censored. There were 36,866 females contributing to this analysis with 14,143 of these having censored records. The median number of females in a contemporary group was six. There were 3,323 sires that had daughters with records. The median number of daughters per sire was seven. Heritability of sustained reproductive success on the underlying scale estimated from these data was approximately 0.05. Additional data accumulated over time will improve this genetic evaluation. Sustained reproductive success is important to the commercial beef industry and results from this evaluation are expected to enhance the assessment of economic value of Hereford seedstock.